This invention relates to the field of borehole telemetry, especially mud pulse telemetry wherein data relating to borehole parameters is gathered by sensing instruments located downhole in the drill string and is transmitted to the surface via pressure pulses created in the drilling mud. More particularly, this invention relates to a shock absorber assembly wherein the mud pulse transmitter and the sensor elements are encased in a single one piece segment of a drill collar, the shock absorber assembly for the mud pulse transmitter being positioned entirely at the top or front end of the drill collar above the mud pulse transmitter, and the entire shock absorber assembly for the sensor elements being positioned at the rear or bottom end of the drill collar entirely below the sensor package.
The basic concept of mud pulse telemetry for transmitting borehole data from the bottom of a well to the surface has been known for some time. United States Pat. Nos. 4,021,774, 4,013,945 and 3,982,431, all of which are owned by the assignee of the present invention, show various aspects of a mud pulse telemetry system which has been under development by the assignee hereof for several years. During the course of development of a mud pulse telemetry system, particular attention has been paid to component mounting and shock absorber assemblies. Mounting and shock absorber assemblies are shown in U.S. Pat. Nos. 3,714,831 and 3,782,464. While the mounting and shock absorber assemblies of those patents are adequate for some purposes, they pose assembly and other problems, and the drill collar in which they are mounted must be in two pieces in order to have access to the shock absorber elements for assembly. The requirement for a two piece drill collar posed by those prior shock absorber assemblies poses several disadvantages. Joints in a drill collar pose several well recognized problems. They result in two different internal diameters, they provide locations for concentration of flex stressing which may lead to structural failure, and they are sources of potential leakage. While joints, of necessity, must occur at the junction of each segment of drill pipe, it is desirable to avoid any more joints than necessary; so it became desirable to develop a mounting and shock absorber system which does not require a split drill collar segment. The prior art has also posed problems in failure to isolate various system components from shock loads imposed on other components.